This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To cause disease, V. cholerae must bind to or colonize the lining of the small intestine. A new colonization factor has been identified for V. cholerae, TcpF. This protein, which is secreted out of the bacteria by the Type IV pilus assembly apparatus, is essential for colonization, yet little is known about its functions. TcpF has an important role in mediating disease for V. cholerae and knowing its atomic structures will provide clues to its function in colonization. In addition, this research will provide a more in depth understanding of how this protein is transported out of the bacteria. These findings may be applied to other bacteria using similar systems. Importantly, these studies may lead to targets for therapeutic and vaccine agents for treatment of disease. Enterotoxigenic E. coli is an important cause of mild to cholerae-like diarrhea. This bacteria colonizes the intestinal epithelium through a variety of distinct colonization factor antigens CFA/I, CFA/II, CFA/III and CFA/IV. The central role CFA/III play in host colonization together with their prominent exposure on the bacterial surface make them attractive targets for vaccines and therapeutics. CFA/III is a polymeric assembly of protein CofA. An understanding of the molecular structure will provide insight into its functions, and allow us to rationally design highly specific anti-bacterial agents.